The present invention relates, in general, to high resolution optical systems, and more particularly to a method and apparatus for the production and use of light beams having diameters in the range of 100 to 500 .ANG.. The invention further relates to optical microscopes having a resolution on the order of 500 .ANG., to methods of studying objects using such a microscope, and to methods of lithography utilizing the high resolution capabilities of the apparatus of the present invention.
With the advance of submicron technology, the need for a light microscope for use in microanalysis of materials has steadily increased. Although electron microscopes are capable of detecting objects with a very high degree of resolution, viewing by this means not only requires that the sample be inserted into a vacuum, but often results in destructive effects on the sample because of the ionizing radiation.
With presently available technology, nondestructive viewing can be obtained using visible light in two different ranges. At the lower end of the scale, fluorescence spectroscopy coupled with chemical methods can be used to determine on a statistical basis the dimensions between objects that are up to about 80 .ANG. apart. At the upper end of the scale, light microscopy, when used in the fluorescence mode, can be used to determine dimensions as small as about one-half the wavelength of the light that is used; that is, down to about 2500 .ANG.. However, separations between objects (or feature dimensions) of between 80 .ANG. and 2500 .ANG. are inaccessible using visible wave lengths. The ability to determine such dimensions using light microscopy is very important since, unlike electron microscopy, samples can be studied in their natural environment without resorting to high vacuum conditions and without the risk of damage. Such a capability is particularly useful in biological applications where clinical testing or chemical mapping are to be done.
Advances in microelectronics are leading to smaller and smaller structures. However, the techniques for fabricating such devices have not kept pace with such developments, and the volume production of microscale devices presents a difficult problem. Optical lithography is, at the present time, limited to the production of features having a size of approximately 1 micron (10000 .ANG.), although improvements using far ultraviolet radiation allows sizes down to one-half micron (5000 .ANG.) to be achieved. To fabricate structures with even smaller sizes, one must resort to electron, ion, or X-ray beam technology.
Although electron and ion beam technology are now the most widely used methods in the microelectronics industry for producing submicron structures, such methods have a relatively low rate of production due to the need to scan the beam across the wafer on which the structure is being formed. X-ray methods are being investigated since a larger production rate may be achievable, although such methods require a dedicated synchrotron source. An extension of optical technology to the half micron size scale would couple the small feature size capability of electron, ion, and X-ray beam technology to the higher rates which are necessary for economical production.